1. Field of the Invention
The invention relates to a double pump unit having two hydraulic pumps with drive shafts coaxially arranged and coupled to each other through the intermediary of a coupling piece, in a force-locking manner.
2. Discussion of the Prior Art
Such a double pump unit is known from DE-OS 33 24 583. The known double pump unit has two hydraulic pumps having drive shafts arranged coaxially with one another, which drive shafts are coupled with one another by means of a coupling piece, in a force-locking manner. The coupling piece is thereby constituted in the form of a hollow shaft and is connected with the free drive shaft ends of the two hydraulic pumps by means of a spline/groove toothing. The coupling piece is surrounded by a connection piece which accommodates the suction channels and pressure channels leading to the hydraulic pumps. The double pump unit known from DE-OS 33 24 583 draws the pressure medium to be delivered directly out of a low-pressure line, without previously subjecting the pressure medium to a pre-compression. Thereby, the efficiency of the known double pump unit is limited and additionally there exists a danger of damage due to cavitation in the suction channel.
In order to counter this danger, it is on the other hand known from DE-PS 30 18 711 to connect a charging pump upstream of a hydraulic pump. The charging pump consists of an impeller formed in the manner of a turbine, which rotates in a correspondingly formed chamber.